Toughened glass, pin type insulator



July 14, 1964 D. R. EDWARDS TOUGHENED GLASS, PIN TYPE INSULATOR Filed Jan. 4, 1961 I I I nvenlor zL/u %v n &ww

United States Patent O 3,14l,063 TQUGHENED GLASS, PIN TYPE INSULATOR Derrlc Robert Edwards, Eccleston, St. Helens, England, assgnor to Pilkington Brothers Limited, Liverpool, England, a corporation of Great Britain Filed Jan. 4, 1961, Ser. No. 80,573 Clams priority, application Great Britain Jan. 5, 1960 Claims. (CI. 174-212) This invention relates to insulators and in particular to a moulded glass insulator blank intended for use in the manufacturing from the blank of a toughened glass insulator designed for supporting an electric power cable.

These insulators usually comprise a hollow head and an integral skirt, or shed, emanating from the head, and it has been proposed to produce in the skirt and near the head an annular barrier portion to prevent propagation through the barrier of a fracture initiated in the skirt beyond the barrier.

A main object of the present invention is to provide an improved form of moulded glass insulator blank which is so designed that when the blank is tempered there is produced a toughened glass insulator having a more effective barrier to fractures than has hitherto been possible.

In accordance with the present invention a glass insulator blank intended for use in the manufacture from the blank of a toughened glass insulator designed for supporting an electric power cable is moulded with a hollow head, a skirt, and an intermediate part joining the head to the skirt, said intermediate part comprising a part of cylindrical form whose axis coincides with the axis of the blank and an annulus extending between the head and the upper end of the said cylindrical part substantially at right angles to the cylindrical part, Whereby on tempering the blank a Stress pattern is induced which arrests in said intermediate part a fracture initiated in the skirt. The lower end of the cylindrical part rnay be joined to the skirt.

Further according to the invention there is provided a glass insulator blank intended for use in the manufacture from the blank of a toughened glass insulator designed for supporting an electric power cable, said blank being moulded with a hollow head, a skirt, and an intermediate part joining the head to the skirt, said intermediate part comprising a part of cylindrical form whose axis coincides with the axis of the blank, an annulus extending between 'the `upper end of the said cylindrical part and the head, and a second annulus extending between the lower end of the said cylindrical part and the skirt, said annuli extending substantially at right angles to the said cylindrical part, whereby on tempering the blank a Stress pattern is induced which arrests in said intermediate part a fracture initiated in the head or in the skirt.

Still further according to the invention the intermediate part may include a second part of cylindrical form coaxial with said first part of cylindrical form and joining the second annulus to the skirt. i

In a preferred Construction according to the invention the glass insulator blank is moulded with a hollow head, a skirt, and an intermediate part joining the head to the skirt, said intermediate part comprising a part of cylindrical form whose axis coincides with the axis of the blank, and an annulus extending between the head and the upper end of the said cylindrical partsubstantially at right angles to the cylindrical part, the lower end of the said cylindrical part being ioined to the skirt and the radial width of the intermediate part being not less than three times ,the average thickness of the glass in the intermediate part, which average thickness is not more than two-thirds of the least thickness of the glass in that part of the head adjacent to the intermediate part.

The invention also comprehends a toughened glass e ce insulator' designed for supporting an electric power cable and manufactured by tempering a glass insulator blank moulded with a hollow head, a skirt and an intermediate part joining the head to the' skirt, said intermediate part comprising a part of cylindrical form whose axis coincides with the' axis of the blank and an annulus extending between the head and the' upper end of the said cylindrical part substantially at right angles to the cylindrical part, so that a Stress pattern is induced in the insulator which arrests in said intermediate part a fracture initiated in the skirt.

In order that the invention may be more clearly understood some embodiments thereof will now be described by way of example, with reference to the accompanying drawings, in which:

FIGURE 1 is a section on a diameter of a glass insulator blank according to the invention,

FIGURE 2 is a section on a diameter of a second glass insulator blank according to the invention, and

FIGURE 3 is a part section showing a modification of the blank of FIGURE 2.

Referring to FIGURE l of the drawings a glass insulator blank intended for use in manufacturing from the blank a toughened glass insulator designed for supporting an electric power cable, is moulded with a hollow head 1 and a skirt indicated generally by the reference number 2. The hollow head 1 is moulded with a groove 3 for a power cable at the top of the head, and just below the top of the head is an annular shoulder 4, below which is an annular recess 5 arranged to receive the usual binding wire or clips for holding the cable in the top groove 3. Alternatively a cable may be carried in the recess 5 and held by a binding wire passing over the top groove 3, for example if the direction of the cable is to be changed.

The skirt 2 is formed with a downwardly extending annular rib 6 which is located inside the lower extremity 7 of the skirt, and the head 1 extends downwardly so that the bottom of the head 1, the rib 6 and the extremity 7 of the skirt lie in the same plane. The inside of the head 1 is moulded with a thread 8 for engagement by a threaded pin on which the insulator is mounted in the well known manner.

The blank is moulded with an intermediate part joining the head to the skirt, the intermediate part comprising a part 9 of cylindrical form whose axis coincides with the aXis of 'the blank and an adjoining annulus 10 extending from the upper end of the said cylindrical part 9 substantially at right angles thereto. The faces of the cylindrical part 9 are substantially parallel, and it will be understood that the part 9, while having a cylindrical form, is very slightiy conical to assist the withdrawal of the press tools when the blank is moulded. The faces of the annulus 10 are substantially parallel, and the annulus 10 .slopes downwardly from the head the slope being sufiicient to enable moisture to drain away from the head. The lower end of the cylindrical part 9 is joined to the skirt 2 in such a way that the inner surface of the cylindrical part 9 continues downwardly to form the inner surface of the annular rib 6.

The total radial width of the intermediate part 9 and 10, is not less than three times the average thickness of the glass in the cylindrical part 9 and the annulus lil, Whichaverage thickness is not more than two-thirds of the thickness of the glass in that part of the head 1 adjacent to the annulus 10. For example, in an insulator blank which is moulded of a soda-lima glass, the coefcient of thermal expansion of which is 82.4 10 per C., and whose 'overall diameter is about 8 inches, the radial width of the intermediate part is about 1 inch, the average thickness of the glass in the intermediate part is about %i inch, and the least thickness of the glass in that e (j part of the head adjacent to annulus is about A; inch.

When the moulded blank shown in FIGURE 1 is tempered, the head 1 and the skirt 2 shrink as the blank is cooled, and a stress pattern is induced in the intermediate part 9, 1& which is such that the propagation of a fracture initiated in the skirt 2 is arrested in the intermediate part. For example, if the skirt is shattered by a blow on its extremity 7, the shattering will not extend completely through the intermediate part and the head will remain unbroken and will continue to support the cable which is attached to it.

The forces applied to the annulus 10 by the shrinkage of the head alone are such that the stress pattern induced in the annulus 1@ by the head alone when the skirt has disintegrated will act as an eicient barrier and will arrest the fracture.

If the head l of the toughened insulator is shattered by a blow, the shattering will usually extend through the intermediate part 10, 9 and the skirt 2 also Will disintegrate. This is an advantage because a breakage of the head 1, which would result in electrical failure can be detected by inspection from ground level and is certain to be seen as the skirt has shattered as well as the head.

The design of the blank illustrated in FIGURE 1 can be modified so that the lower end of the cylindrical part 9 joins the skirt at a position between the rib 6 and the extremity 7 of the skirt, for example midway between the rib 6 and the extremity 7.

Another embodiment of the invention is shown in FIG- URE 2 in which the lower end of the part 9 of cylindrical form is joined to the skirt by a second annulus 11 which extends substantally at right angles to the cylindrical part 9. The blank of FIGURE 2 is otherwise similar to that illustrated in FIGURE 1 and when the blank of FIG- URE 2 is tempered the stress pattern induced in the intermediate part which consists of the annulus lt), the cylindrical part 9 and the second annulus 11, is such that the propagation of a fracture initiated either in the head or the skirt is arrested in the intermediate part. If the skirt 2 disintegrates the stress pattern induced in the intermediate part by the shrinkage of the head alone is sufficent to prevent the propagation of a fracture through the intermediate part to the head. If the head 1 of the toughened insulator is shattered by a blow, the propagation of the shattering will be arrested within the intermediate part 9 and 11, and the skirt 2 Will remain unbroken.

In a further embodiment the blank shown in FIGURE 2 is modified, as shown in FIGURE 3, so that the intermediate part includes a second part 12 of cylindrical form coaxial with the first part 9 of cylindrical form. The upper end of the second cylindrical part 12 is joined to the second annulus 11, and its lower end is joined to the skirt in the manner shown for the cylindrical part 9 in FIGURE 1. Alternatively the second cylindrical part 12 is joined to the skirt at a point between the rib 6 and the extremity 7 of the skirt, for example midway between the rib 6 and the extremity 7.

In preferred constructions of the moulded blanks just described with reference to FIGURES 2 and 3 the radial width of the intermediate part which joins the head to the skirt is not less than three times the average thckness of the glass in the intermediate part, which average thickness is not more than two-thirds of the least thckness of the glass in that part of the head adjacent to the intermediate part.

In the three embodiments of the invention illustrated respectively in FIGURES 1, 2 and 3 the regions where the parts of the intermediate part extend into each other have a sharp curvature.

That is in FIGURE 1 the radius of the curve joining the cylindrical part 9 to the annulus 10 is short so that the curvature is sharp. Similarly the curvature is sharp in the regions where the cylindrical part 9 extends into the annuli 1@ and 11 in FIGURE 2, and where the cylindrical parts 9 and 12 extend into the annuli 10 and 11 in FIGURE 3.

By moulding a glass insulator blank with any one of the shape described above and then tempering the blank, there is provided a toughened glass insulator with an effective barrier zone, which has hitherto been impossible.

I claim:

1. A moulded glass insulator blank intended for use in the manufacture from the blank of a toughened glass insulator designed for supporting an electric power cable, said blank consisting of a hollow head closed at the top and formed with a central cavity opening at the bottom of the head, a skirt extending radially and downwardly around the head and having a radially-extending upper portion, and an intermediate part joining the head to said radially-extending upper portion of the skirt, which intermediate part comprises a part of cylindrical form whose axis coincides with the axis of the blank and an annulus extending from the head substantally at right angles to said axis and merging into the upper end of the cylindrical part through an integral annular part of curved crosssection, which shape of the blank is such that on tempering the blank a stress pattern is induced which arrests in said intermediate part a fracture initiated in the skirt.

2. A moulded glass insulator blank according to claim l, wherein the lower end of the said cylindrical part is joined to the radially-extending upper portion of the skirt.

3. A moulded glass insulator blank intended for use in the manufacture from the blank of a toughened glass insulator designed for supporting an electric power cable, said blank consisting of a hollow head closed at the top and formed with a central cavity opening at the bottom of the head, a skirt extending radially and downwardly around the head and an intermediate part joining the head to the skirt, which intermediate part comprises a part of cylindrical form whose axis coincides with the axis of the blank, an annulus extending substantally at right angles to said axis between the upper end of the said cylindrical part and the head, and a second annulus extending substantally at right angles to said axis between the lower end of the said cylindrical part and the skirt, said annuli respectively merging into the upper and lower ends of the cylindrical part through integral annular parts of curved cross section, which shape of the blank is such that on tempering the blank a stress pattern is induced which arrests in said intermediate part a fracture initiated in the head or in the skirt.

4. A modification of a glass insulator blank according to claim 3, wherein the intermediate part includes a second part of cylindrical form co-axial with said first part of cylindrical form, which second cylindrical part joins the second annulus to the skirt and merges into the second annulus through an integral annular part of curved cross section.

5. A moulded glass insulator blank intended for use in the manufacture from the blank of a toughened glass insulator designed for supporting an electric power cable, said blank consisting of a hollow head closed at the top and formed with a central cavity opening at the bottom of the head, a skirt extending radially and downwardly around the head, and an intermediate part joining the head to the skirt, which intermediate part comprises a part of cylindrical form whose axis coincides with the axis of the blank and whose lower end is joined to the skirt, and an annulus extending from the head substantally at right angles to said axis and merging into the upper end of the cylindrical part through an integral annular part of curved cross-section, the radial width of the intermediate part being not less than three times the average thckness of the glass in the intermediate part, which average thickness is not more than two-thirds of the least thckness of the glass in that part of the head adjacent to the intermediate part, which shape of the blank is such that on ternpering the blank a stress pattern is induced which arrests in said intermediate part a fracture initiated in the skirt.

6. A toughened glass insulator designed for supporting an electric power cable, consisting of a hollow head closed at the top and formed with a central cavity opening at the bottom of the head, a skirt extendng radially and downwardly around the head and having a radially-extending upper portion, and an intermediate part joining the head to said radially-extendng upper portion of the skirt, which intermediate part comprises a part of cylindrical form whose axis coincides with the axis of the blank and an annulus extending from the head substantially at right angles to said axis and merging into the upper end of the cylindrical part through an integral annular part of curved cross-section, the Stress pattern in the toughened insulator being such as to arrest in said intermediate part a fracture initiated in the skirt.

7. A toughened glass insulator according to claim 6, wherein the lower end of the said cylindrical part is joined to the radially-extendng upper portion of the skirt.

8. A toughened glass insulator designed for supporting an electric power cable, consisting of a hollow head closed at the top and formed with a central cavity opening at the bottom of the head, a skirt extending radially and down- Wardly around the head, and an intermediate part joining the head to the skirt, which intermediate part comprises a part of cylindrical form whose axis coincides with the axis of the blank, an annulus extending substantially at right angles to said aXis between the upper end of the said cylindrical part and the head, and a second annulus extending substantially at right angles to said axis between the lower end of the said cylindrical part and the skirt, said annuli respectively merging into the upper and lower ends of the cylindrical part through integral annular parts of curved cross-section, the stress pattern in the toughened insulator being such as to arrest in said intermediate part a fracture initiated in the head or in the skirt.

9. A toughened glass insulator according to claim 8,

wherein the intermediate part includes a second part of cylindrical form co-axial with said first part of cylindrical form, which second cylindrical part joins the second annulus to the skirt and merges into the second annulus through an integral annular part or" curved cross section.

10. A toughened glass insulator designed for supporting an electric power cable, consisting of a hollow head closed at the top and formed with a central cavity opening at the bottom of the head, a skirt extending radially and downwardly around the head and an intermediate part joining the head to the skirt, which intermediate part comprises a part of cylindrical form whose axis coincides with the axis of the blank and whose lower end is joined to the skirt, and an annulus extending from the head substantially at right angles to said axis and merging into the upper end of the cylindrical part through an integral annular part of curved cross-section, the radial width of the intermediate part being not less than three times the average thickness of the glass in the intermediate part, which average thickness is not more than tWo-thirds of the least thickness of the glass in that part of the head adjacent to the intermediate part, the Stress pattern in the toughened insulator being such as to arrest in said intermediate part a fracture initiated in the skirt.

References Cited in the file of this patent UNITED STATES PATENTS 834,084 Steinberger Oct. 23, 1906 1,712,860 Weimar May 14, 1929 2,135,359 Taylor et al. Nov. 1, 1938 2,418,713 Holmes et al Apr. 8, 1947 2,870,244 Jellyman et al. Jan. 20, 1959 FOREIGN PATENTS 476,401 Great Britain Dec. 3, 1936 

1. A MOULDED GLASS INSULATOR BLANK INTENDED FOR USE IN THE MANUFACTURE FROM THE BLANK OF A TOUGHENED GLASS INSULATOR DESIGNED FOR SUPPORTING AN ELECTRIC POWER CABLE, SAID BLANK CONSISTING OF A HOLLOW HEAD CLOSED AT THE TOP AND FORMED WITH A CENTRAL CAVITY OPENING AT THE BOTTOM OF THE HEAD, A SKIRT EXTENDING RADIALLY AND DOWNWARDLY AROUND THE HEAD AND HAVING A RADIALLY-EXTENDING UPPER PORTION, AND AN INTERMEDIATE PART JOINING THE HEAD TO SAID RADIALLY-EXTENDING UPPER PORTION OF THE SKIRT, WHICH INTERMEDIATE PART COMPRISES A PART OF CYLINDRICAL FORM WHOSE AXIS COINCIDES WITH THE AXIS OF THE BLANK AND AN ANNULUS EXTENDING FROM THE HEAD SUBSTANTIALLY AT RIGHT ANGLES TO SAID AXIS AND MERGING INTO THE UPPER END OF THE CYLINDRICAL PART THROUGH AN INTEGRAL ANNULAR PART OF CURVED CROSSSECTION, WHICH SHAPE OF THE BLANK IS SUCH THAT ON TEMPERING THE BLANK A STRESS PATTERN IS INDUCED WHICH ARRESTS IN SAID INTERMEDIATE PART A FRACTURE INITIATED IN THE SKIRT. 